These guys are partially idiots. Obviously there is more demand than road if use is directly proportional to supply as they claim. The problem is the way we design cities and lay out the roads. A regular grid where we put STOP lights? seriously? Go, stop, go, stop. And then we put businesses right on the corners to increase congestion right where it's already bad. When cars get tested for EPA MPG ratings, the average speed on the city drive cycle is slightly under 20mph due to all the stop and go. Hybrid cars get better city mpg than highway by using regenerative braking to recover energy from all that stopping and making drag the dominant factor. I don't think traffic circles are relevant, but designing the layout to minimize disruptions to flow altogether. I've been contemplating this a lot, but can't write it all here right now. Imagine if every drive were 10-20 percent longer distance, but you could average twice the speed over the journey! You'd save gas and time. And if your journey takes less time, that's fewer car-minutes on the road which means less traffic and they could have fewer lanes. The problem is even if we could do the design correctly, nobody is going to build a city from scratch - except in China maybe.
Building a city from scratch and designing it primarily with private automobile traffic in mind is a textbook case of Doing It Wrong. The only sane approach would be to build a subway (or maybe streetcars that have right-of-way) and then stick a city on top of it.
It seems like you're assuming that the only priority is moving cars around - not walkability or livability. In other words it seems you're assuming the only purpose of the built environment is to move cars. I argue that it isn't and in that case we should measure other stuff besides moving cars efficiently when building our cities.
No, I advocate efficiency as a goal weather it be cars, public transit, or something else. Personally I'd like easy access to both. But public transit is only viable with high density and I don't like the way we do dense either.
I envision traffic as a viscous fluid. Unlike fluids that we are used to, like flowing water, maple syrup, or honey, this fluid wants to flow in multiple directions at once. If you can imagine a stream that flows both uphill and downhill at the same time, and sometimes acts like thick molasses, other times like corn starch suspension, and other times like mercury, you are ready to think about traffic.
This bizarre fluid does obey certain rules, which are consistent and discoverable. Once you have all the rules, you can model an entire system and run experiments.
That said, I hate roundabouts. They seem to combine the worst elements of multiple solutions to make all drivers equally unhappy and inconvenienced. It is somehow okay that no one wins, because everyone loses.
